The present invention relates to a process for the presulphurization of a hydrocarbon treatment catalyst and/or preconditioning a catalyst which is then sulphurized.
It is often desirable to carry out a sulphurization (generally called presulphurization) of metals occurring in the composition of certain hydrocarbon refining and/or hydroconversion catalysts, either when these catalysts are new, or following regeneration of said catalysts prior to the reuse thereof.
Therefore a presulphurization of new or regenerated catalysts is desirable for the use of said catalysts in refining reactions, e.g. hydrodesulphurization reactions of various petroleum fractions, e.g. gas oils, whose sulphur content should be lowered before use in order to make them comply with specifications. Such desulphurization reactions are generally performed in the presence of hydrogen, the charge being e.g. an atmospheric gas oil generally distilling between 230.degree. and 350.degree. C. and which can have a sulphur content between 0.12 and 1.5% by weight. In this case, the catalyst used for the hydrodesulphurization contains a generally non-acid support, e.g. an alumina or alumina mixtures (U.S. Pat. No. 4,334,982) or any other adequate support based on at least one oxide of a metal or metalloid e.g. magnesia (U.S. Pat. No. 4,132,632/U.S. Pat. No. 4,140,626), silica, silica-alumina, silica-magnesia, fluorinated alumina or silica, alumina-boron, clay, charcoal. The said support mixture or mixtures can at least partly be in amorphous or crystalline form (zeolite) and the catalyst also contains 0.2 to 30% of at least one active metal from groups VI, VIII, etc., e.g. chosen from cobalt, molybdenum, nickel and tungsten (U.S. Pat. No. 3,732,155 and U.S. Pat. No. 3,804,748). Generally use is made of a pair of these metals, e.g. cobalt-molybdenum, nickel-molybdenum or nickel-tungsten. It is possible to use a precious metal from group VIII from the platinum group: Pt, Pd, etc., (U.S. Pat. No. 4,098,682).
Thus, prior to using the new or regenerated catalyst, in the prior art it undergoes a sulphurization (presulphurization) in a hydrodesulphurization reactor. This sulphurization makes it possible to include in the catalyst e.g. approximately 50 to 150% of the stoichiometric quantities of sulphur calculated on the sulphide quantities of formula (according to the metals present): Co.sub.9 S.sub.8, MoS.sub.2, WS.sub.2, Ni.sub.3 S.sub.2.
This sulphurization or presulphurization is carried out in the prior art at a final temperature generally between 250.degree. and 400.degree. C. by a hydrogen sulphide mixture generally diluted in hydrogen (hydrogen sulphide proportion in the hydrogen approximately 0.5 to 5 volume %) with an adequate space velocity of e.g. approximately 1000 to 3000 liters of gas under normal temperature and pressure conditions per liter of catalyst and per hour (U.S. Pat. No. 4,334,982). The actual sulphurization or presulphurization can be carried out in temperature ranges (FR-B-2,476,118). It is possible to use various sulphurizing agents, other than hydrogen sulphide (H.sub.2 S) and e.g. a sulphur compound from the mercaptan group, carbon sulphide (CS.sub.2), sulphides, disulphides or polysulphides, thiophene compounds and preferably dimethyl sulphide (DMS) and dimethyl disulphide (DMDS).
However, catalyst regeneration is ever more frequently taking place on the premises of catalyst regenerating specialists sometimes remote from the industrial unit. The refiner requires a product which is ready to use and this is made possible by the effective process of EP-B-130,850 of the present Applicant, in which a sulphur compound is incorporated into the catalytic material and said compound causes the sulphurization or presulphurization of the catalyst when, subsequently, in the reaction zone (charge treatment zone) or in the immediate vicinity thereof, the catalyst will be contacted with the hydrogen. Obviously, the incorporation of said sulphur compound can, if desired, be carried out in the vicinity of the industrial unit or even at the catalyst treatment location. The incorporation process for said sulphur compound can be performed ex situ, also on a new or regenerated catalyst, prior to the use thereof in an industrial unit.
More specifically, in EP-B-130,850, the catalyst sulphurization process is characterized by a preliminary stage of incorporation into the catalytic material of a sulphur compound of a special nature. The preliminary stage of introducing a sulphur compound, which is referred to in arbitrary manner as ex situ pretreatment, no matter whether it is performed in the vicinity of the industrial unit or at a varying geographical distance therefrom (where the catalyst has been regenerated or produced) does not take place in or in the immediate vicinity of the reactor (called in arbitrary manner in situ), i.e. in areas making it necessary to operate under temperature, pressure or other conditions at least partly imposed by the operating conditions of the actual reactors.
Thus, EP-B-130,850 relates to a process making it possible to incorporate, in the absence of hydrogen, at least one sulphurizing agent of general formula R--S.sub.(n) --R', in which R, R' and n are defined hereinafter, into the pores of the new or regenerated catalyst. The sulphurization of the catalyst can thus be carried out in the following way. In a first stage performed ex situ and in the absence of hydrogen, the catalyst is treated with the aid of at least one sulphurizing agent so as to partly or totally incorporate said agent into the catalyst pores, the sulphurizing agent being a polysulphide of general formula R--S.sub.(n) --R', said sulphurizing agent being used in solution in a solvent. In a second stage, performed in situ and preferably at above 150.degree. C., the catalyst is activated in the presence of hydrogen, the requisite sulphur quantity being fixed as a result of the presence of hydrogen on the metal or metals entering into the composition of said catalyst. This latter stage is improved in EP-G-181,254. The object of these two patents is therefore to carry out ex situ the presulphurization of the catalysts by incorporating the necessary sulphur quantity and only that sulphur quantity which is required by the user. Therefore the catalysts are supplied to the refinery or any other unit preconditioned for sulphurization.
The refiner or any other user consequently only has to reactivate this catalyst in the presence of hydrogen and at a temperature of e.g. 100.degree. to 400.degree. C. for a desulphurization catalyst in order to react the sulphur on the metals contained and immediately start the hydrocarbon refining or conversion reaction by the injection of the charge to be treated.
In the polysulphide of formula R--S.sub.(n) --R', n is an integer from 3 to 20, preferably 3 to 8 and more particularly 5 to 7, R and R', which are the same or different, represent organic radicals, each containing 1 to 150, preferably 2 to 60 and more particularly 4 to 13 carbon atoms per molecule, said radicals being chosen from within the group constituted by alkyl radicals, i.e. saturated or unsaturated, straight or branched or of the naphthene type, aryl radicals, alkyl aryl radicals and aryl alkyl radicals, whereby said radicals can have at least one heteroatom and R' can optionally be a hydrogen atom.
Reference is made as a preferred example of a polysulphide to ditert. dodecyl polysulphide (n=5), in which R and R' are in each case a tert. dodecyl radical. This product is e.g. marketed by ATOCHEM under the reference TPS 32, because it contains approximately 32% by weight sulphur. Reference can also be made to ditert. nonyl polysulphide (n=5), in which R and R' are in each case a tert. nonyl radical. This product is marketed by ATOCHEM under the reference TPS 37 or TNPS, because it contains approximately 37% by weight sulphur.
The sulphurizing agent is used diluted in an adequate solvent and incorporated into the catalyst generally by an impregnation method. The sulphurization processes vary as a function of the fractions to be subsequently treated in the presence of the catalysts treated according to the invention. The chosen solvent can thus be one of the following solvents used singly or in mixed form:
a light petrol e.g. boiling at between approximately 60.degree. and 95.degree. C., PA1 a hexane-type petrol boiling at approximately 63.degree. to 68.degree. C., PA1 a F-type petrol boiling at approximately 100.degree. to 160.degree. C. and generally containing 10 to 20% and e.g. 15 volume % of aromatic hydrocarbons, PA1 a white spirit-type petrol boiling at between approximately 150.degree. and 250.degree. C. and generally containing 14 to 22 and e.g. 17 volume % aromatic hydrocarbons, PA1 any hydrocarbon or non-hydrocarbon fraction, equivalent to the above petrols, PA1 or any other appropriate organic solvent.
It has subsequently been discovered (EP-A-400,581) that the qualities of the methods described in EP-B-130,850 and EP-B-181,254 of the Applicant are further improved if the organic polysulphide is used mixed in critical quantities with elemental sulphur instead of being used alone. (The use of elemental sulphur alone for the presulphurization of catalysts is described in U.S. Pat. No. 4,177,136). The simultaneous use of elemental sulphur brings about a synergism in the ex situ presulphurization, when said elemental sulphur is mixed with an organic polysulphide. The elemental sulphur is e.g. used in the form of melted sulphur, powder sulphur, flowers of sulphur, according to any appropriate method, e.g. that described in EP-B-153,233 of the present Applicant.